Re: Speed, Distance, Time

SDT # 2

Two trains are running at 40 km/hour and 20 km/hour respectively in the same direction. The faster train completely passes a man in the slower train in 5 seconds. What is the length of the faster train?

Re: Speed, Distance, Time

Re: Speed, Distance, Time

SDT # 3

An express train traveling at 72 km/hr speed crosses a goods carriage train traveling at 45 km/hr speed in the opposite direction in half a minute. Alternatively, if the express train were to overtake the goods carriage train, how long will it take to accomplish the task? Assume that the trains continue to travel at the same respective speeds as mentioned in the earlier case.

Re: Speed, Distance, Time

SDT # 4

X is picked up by his father by car from school everyday and they reach home at 5.00 p.m. One day, since the school got over an hour earlier than usual, he started walking towards home at 3 km/hr. He met his father on the way and they reached home 15 minutes earlier than their usual time. What is the speed of the car?

Re: Speed, Distance, Time

SDT # 5An hour after Allan started from his college towards Cindy's home, a distance of 53 km, Cindy started from her home on the same road towards Allan's college. If Allan's speed was 4 km per hour and Cindy's was 3 km per hour, how many kilometres from Cindy's home did the two meet?

Re: Speed, Distance, Time

SDT #4

I like this one! Some good red herrings. Started off thinking about what time dad left home; what is the distance from school to home? did dad always manage to arrive exactly on time? why did he call his son "X"? Actually, none of it is relevant (but I do feel sorry for the poor boy branded with such a name)

Re: Speed, Distance, Time

SDT # 3 is correct! Well done, ashwil! I don't remember the answer to the next problem, nor do I have the time to check your solution now. I shall try SDT#4 later before telling whether you are right or wrong! Well done, ashwil

Re: Speed, Distance, Time

Re: Speed, Distance, Time

ganesh wrote:

SDT # 4

X is picked up by his father by car from school everyday and they reach home at 5.00 p.m. One day, since the school got over an hour earlier than usual, he started walking towards home at 3 km/hr. He met his father on the way and they reached home 15 minutes earlier than their usual time. What is the speed of the car?

The car arrives at 5.00 pm at point 'S'. But since Mr X started walking at4.00 pm, they will meet at a point 'M'.

The car saved travel distance M -> S and S -> M. This resulted in 15 minutessavings. Assuming uniform speed, it takes 7 1/2 minutes from 'M' to 'S' andvice-versa. So both meet at 4:52 1/2 pm. The Son had been walking from 4.00 pmtill this time, which is 52 1/2 min.

The same distance is covered by the car in just 7 1/2 min. Therefore the cartravels at 52.5/7.5 times the walking speed of Mr X (3 km/hr).

Re: Speed, Distance, Time

Re: Speed, Distance, Time

A thief escaped from police custody. His speed is 40 km/hr. The police realized it after 3 hr and started chasing him in the same direction at 50km/hr. The police had a dog which could run at 60 km/hr. The dog would run to the thief and return to the police and then would turn back towards the thief and so on until the thief is caught. Find the total distance travelled by the dog in the direction of the thief.

Re: Speed, Distance, Time

In 3 hrs the thief has run 120 km. Relative speed of thief and police is 10 kmph. So, police will take 12 hrs to catch the thief and thus the dog will run for the same amount of time (no matter in what direction!)!Hence, the total distance travelled by the dog is 12*60=720 km!

Re: Speed, Distance, Time

ZHero wrote:

In 3 hrs the thief has run 120 km. Relative speed of thief and police is 10 kmph. So, police will take 12 hrs to catch the thief and thus the dog will run for the same amount of time (no matter in what direction!)!Hence, the total distance travelled by the dog is 12*60=720 km!

720 is the total distance covered by dog, the question asks the distance covered by dog in direction of the thief... you have to remove the distance which dog covered coming back to police each time after seeing the thief...

Re: Speed, Distance, Time

Aah! Got it!When running towards the thief, the relative speed of dog is 60-40=20 kmph and when running back towards the police, the relative speed is 60+50=110 kmph!Now, the total distance travelled by dog i.e. 720 km is travelled with two speeds of 20 kmph and 110 kmph in 12 hrs! Let x be the time for which he runs in the thieves direction!Hence, 110(12-x)+20x=720x=20/3Therefore, distance travelled in the direction of thief is 60*20/3=400 km !!

Re: Speed, Distance, Time

Rohan fires two bullets from the same place at an interval of 12 minutes but Raju sitting in a train approaching the place hears the second report 11 minutes 30 seconds after the first. What is the approximate speed of train (if sound travels at the speed of 330 meters per seconds)?

Re: Speed, Distance, Time

hi ganesh

Here lies the reader who will never open this book. He is forever dead.Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and PunishmentThe knowledge of some things as a function of age is a delta function.